CODEWITHSUNDEEP
linuxdockercontainersalpine-linux
Ole
Ole

Reputation: 47222

Starting a shell in the Docker Alpine container

To start an interactive shell for the Ubuntu image we can run:

ole@T:~$ docker run -it --rm ubuntu
root@1a6721e1fb64:/# ls
bin  boot  dev  etc  home  lib  lib64  media  mnt  opt  proc  root  run  sbin  srv  sys  tmp  usr  var

But when this is run for the Alpine Docker image, the following results:

ole@T:~$ docker run -it --rm alpine
Error response from daemon: No command specified

What is the command for starting an interactive shell in an Alpine base container?

Upvotes: 263

Views: 328292

Answers (4)

Marcos
Marcos

Reputation: 866

In case the container is already running:

docker exec -it container_id_or_name ash

Upvotes: 44

valiano
valiano

Reputation: 18661

Nowadays, Alpine images will boot directly into /bin/sh by default, without having to specify a shell to execute:

$ sudo docker run -it --rm alpine  
/ # echo $0  
/bin/sh

This is since the alpine image Dockerfiles now contain a CMD command, that specifies the shell to execute when the container starts: CMD ["/bin/sh"].

In older Alpine image versions (pre-2017), the CMD command was not used, since Docker used to create an additional layer for CMD which caused the image size to increase. This is something that the Alpine image developers wanted to avoid. In recent Docker versions (1.10+), CMD no longer occupies a layer, and so it was added to alpine images. Therefore, as long as CMD is not overridden, recent Alpine images will boot into /bin/sh.

For reference, see the following commit to the official Alpine Dockerfiles by Glider Labs:
https://github.com/gliderlabs/docker-alpine/commit/ddc19dd95ceb3584ced58be0b8d7e9169d04c7a3#diff-db3dfdee92c17cf53a96578d4900cb5b

Upvotes: 48

Ole
Ole

Reputation: 47222

ole@T:~$ docker run -it --rm alpine /bin/ash
(inside container) / #

Options used above:

  • /bin/ash is Ash (Almquist Shell) provided by BusyBox
  • --rm Automatically remove the container when it exits (docker run --help)
  • -i Interactive mode (Keep STDIN open even if not attached)
  • -t Allocate a pseudo-TTY

Upvotes: 457

jansanchez
jansanchez

Reputation: 1229

Usually, an Alpine Linux image doesn't contain bash, Instead you can use /bin/ash, /bin/sh, ash or only sh.

/bin/ash

docker run -it --rm alpine /bin/ash

/bin/sh

docker run -it --rm alpine /bin/sh

ash

docker run -it --rm alpine ash

sh

docker run -it --rm alpine sh

I hope this information helps you.

Upvotes: 102

Related Questions